The present invention relates to an ink-jet printer and print control method thereof and, more particularly, to an ink-jet printer of a dot-matrix print scheme for printing by rasterizing n-valued (n.gtoreq.3) quantization data (n valued; n is a natural number) onto an L (horizontal).times.M (vertical) matrix, and print control method thereof.
Various color print schemes that are currently known include a thermal transfer scheme for transferring ink of an ink ribbon by heat energy, an ink-jet print scheme for printing by making ink droplets fly and attach to a printing medium such as paper or the like, and the like.
In such color print schemes, especially, the ink-jet print scheme is a non-impact print scheme free from any noise produced upon printing, can achieve high-speed printing, and can print on normal paper without requiring any dedicated fixing process. Also, since the apparatus arrangement is relatively simple, a color system can be easily implemented.
In recent years, it has been attempted to use ink-jet printers with these advantages to form higher-quality images by increasing the resolution of printed images using ink droplets having smaller sizes.
However, as the resolution of a printed image becomes higher, the data size to be processed in the apparatus becomes huge. In a print system including a host apparatus such as a computer and an ink-jet printer, low data processing speed in the host apparatus or low data transfer speed upon transferring data from the host apparatus to the printer considerably lowers the throughput of the overall system.
Furthermore, as the resolution of a printed image becomes higher, the memory size required in the ink-jet printer main body must be increased, resulting in an increase in apparatus cost.
For this reason, when an image to be printed by the ink-jet printer has priority on the grayscale (the number of colors) over the resolution like a photograph, the host apparatus transfers image data which has a relatively low resolution and has undergone a multi-valued quantization process (to be referred to as highly-quantized image data hereinafter) to the printer, and rasterizes the received low-resolution, highly-quantized image data on a predetermined matrix, thus implementing so-called dot-matrix printing.
For example, assuming that the host apparatus quantizes image data to 9-valued (4-bit) data at a resolution of 300 (horizontal).times.300 (vertical) DPI (dot per inch), and the printer prints by rasterizing that quantized image data at 1,200 (horizontal).times.600 (vertical) DPI (4.times.2 matrix), since the process in the host apparatus is done at 300 DPI, the load on the host apparatus can be reduced. Since 300-DPI, 4-bit image data corresponds to 600.times.600 DPI, 1-bit image data, the data size to be transferred to the printer can be half that of 1,200.times.600 DPI, 1-bit image data. Hence, the size of a reception buffer required in the printer can be halved.
However, when an ink-jet printer, which sets a printing resolution as relatively high as 1,200 (horizontal).times.600 (vertical) DPI, prints an image by dot-matrix printing, the following problems are posed.
That is, as a matrix pattern for rasterizing image data which has been quantized to 9-valued data at a resolution of 300.times.300 DPI onto a 4.times.2 matrix, one fixed pattern is used for a predetermined grayscale level. Hence, since an identical matrix pattern is used on an image on which an identical grayscale level appears continuously, periodic nonuniform or stripe patterns appear on the actually printed images due to errors of ejection precision of ink droplets by a printhead, paper feed precision of the printer main body, or feed precision of a carriage.
Since a predetermined grayscale level is expressed using an identical dot pattern, pseudo edges appear in the printed image if such dot pattern is continuously used.